Method and device for banding a stack of wide, flat products

ABSTRACT

For banding a stack of wide, flat products, a strap is completely wound around the stack. Before the strap is tensioned, at least two stops are positioned on or near to the stack, which limit the tensioning movement of the strap and to which the strap is applied in the tensioned condition. The stops and the banded stack are subsequently separated from each other. The stops are repositioned relative to each other after fixture of the strap and before separation from the stack. A device for performing the method has a tensioning unit using at least two stops to limit the tensioning movement of a strap and to which the strap can be applied in the tensioned condition. The stops can be repositioned relative to each other.

This application claims Paris Convention priority of DE 10 2012 007 773.4 filed Apr. 20, 2012 the complete disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for banding a stack of wide, flat products with a strap, wherein the strap is wound completely around the stack and then a tensile force is exerted on the strap, whereby the strap is tensioned inward onto the stack, and wherein the strap is then fixed in the tensioned condition, wherein, before the strap is tensioned, at least two stops are positioned on or near the stack that limit the tensioning movement of the strap and wherein the stops and the banded stack are subsequently separated from each other.

The invention also relates to a device for banding a stack of wide, flat products with a strap, with a tensioning unit, by means of which the strap is completely wound around the stack, can be tensioned onto the stack from the outside, and can be fixed, and can limit, with at least two stops, the tensioning movement of the strap and to which the strap can be applied in the tensioned condition.

In particular, in logistics and transportation technology, the problem is often encountered that numerous flat, wide products, for example, envelopes or brochures have to be grouped together as a stack to form a transportation unit, wherein the stack is banded with a plastic strap in a banding machine and thus held together.

The description below uses a stack of envelopes as an example. The invention is, however, not restricted to this application and can also be applied to a stack of other flat, wide products in the same way.

After a stack of envelopes has been put together, the strap is wound completely around the stack and a tensioning or tensile force is exerted on the strap, whereby the strap is tensioned onto the stack from the outside and thus holds it together. The strap usually consists of a relatively flexible plastic, in particular, made of polypropylene, polyester, or PET, and is fixed in the tensioned condition, for example, by welding or in another manner.

To achieve the tension in the strap when the tensile force is applied, a counter-support is required that is formed by the stack, that is, the internal stability of the stack. However, if the stack is relatively small, for example, containing only two envelopes, the internal stability of the stack is so slight that the tensioning force of the strap pulls together and crumples the envelopes during tensioning. The strap may even tear into the envelopes and damage them.

Banding a stack of flat, wide products in the manner described is therefore only possible if the stack has a sufficient height and therefore sufficient internal stability. The method cannot be used in automated systems in this way because it is not possible to predict how many products a stack, for example, of envelopes, will contain.

U.S. Pat. No. 2,418,550 describes the stacking of soft, flexible medical compresses. The stack is initially put together and then pressed from above and fixed, whereupon a tensioning bow with lower stop fingers and upper stop fingers is inserted laterally until the stack is held between the stop fingers. A strap is then wound around the stack and the stop fingers, drawn tight, and fixed. The tensioning bow with the stop fingers is then pulled out. The tensioned and fixed strap exerts a high tensioning or clamping force on the stop fingers. It has been found that subsequent separation of the stack from the stop fingers frequently results in problems if the strap has been applied with a large tensioning force so that a strong clamping effect exists between the strap and the stop fingers.

The object of the invention is to provide a method for banding a stack of wide, flat products wherein the stack and the stops can be easily separated.

It is also an object of the invention to provide a device with which the method can be applied in a simple manner.

SUMMARY OF THE INVENTION

This object is achieved by a method with the characteristics of the independent claim. The stops are repositioned relative to each other before separation from the stack.

The invention is also based on the basic idea of using not only the internal stability of the stack as a counter-support for the tensile force of the strap but at least one and preferably two stops that prevent the stack from being pushed together or crumpled by the tensile force of the strap. Before the strap is tensioned, the stops are positioned near to or on the stack. The strap is then wound around both the stack and the stops at the same time and drawn tight. Drawing the strap tight pulls it inwardly up against the stack and also the stops. The stops are sufficiently stable that they can take up and dissipate the tensioning force of the strap. Because of the stops, the tensioning movement of the strap is not limited by the stability of the stack but by the position of the stops, which ensures that the stack retains its shape even in the tensioned condition.

This enables the inventive method to also be applied reliably irrespective of the internal stability of the stack. After application of the tensioning force, the strap is usually fixed in the tensioned condition. After fixture, the stops are no longer necessary and can be separated from the banded stack. This can be done both by withdrawing the stops and by pulling the stack banded with the strap from the stops.

After the stack has been banded and the strap has been fixed, the stack and the stops are separated from each other in the manner described above. Because the stops have limited the tensioning movement of the strap during tensioning, the strap is still applied to the stops with a relatively high tension. To make it easier to remove the stack from the stops, according to the invention the stops are repositioned relative to each other before the stack is pulled off. To achieve the relative repositioning of the stops, it is possible for only one of the stops to be repositioned while the other stop retains its position. Preferably, however, both stops are repositioned.

In one possible embodiment of the invention, the relative repositioning of the stops is effected by moving the stops away from each other. Alternatively or additionally, the stops can be moved toward each other. In an especially preferred embodiment of the invention, the stops are first moved away from each other and then toward each other.

Because of the movement away from each other, the stops overshoot the outer contour of the stack in the outward direction and further tension the already tensioned strap until the strap is locally overextended in the regions where it is in contact with the stops. The overextension of the strap reduces the strain it exerts on the stack when the stops are returned to their original position so that the stack can more easily be removed from the stops.

The strap, which consists of plastic, for example, polypropylene, exhibits high internal stability so that no sharp deflection of the strap is caused when a tensile or tensioning force is applied. In the case of a stack that only consists of two envelopes the problem can occur that the strap is unable to follow the contour of the stack at the edges of the stack, but instead forms a loop. To avoid this problem, in a further embodiment of the invention, the straps can be repositioned relative to each other after fixture of the strap in such a way that the strap is locally overextended and plastically deformed. Due to the local overextension of the strap, a sharp deflection of the strap is formed at this point, for example, through 360° with the result that the strap lies closely against the stack even in the case of very thin stacks. The local overextension of the strap is achieved because the stops move away from each other.

If the stops move toward each other so that at least one stop and preferably both stops are disposed offset from the edge of the stack toward the center thereof, the strap exerts no or a much reduced force on the stops. This makes it considerably easier to subsequently separate the stack from the stops.

The stops are preferably positioned in edge regions of the stack on opposite sides. In particular, the stops are each disposed flush with one side edge of the stack before the strap is tensioned. The stops can be constituted as plate-like fingers onto which the stack is placed in such a way that the outer edges of the fingers facing away from each other each coincide with an outer edge of the stack.

The object stated above is achieved with a device having a tensioning unit using at least two stops that limit the tensioning movement of the strap and to which the strap can be applied in the tensioned condition, wherein the stops can be repositioned relative to each other. Therein, in particular, the distance between the stops can be enlarged and/or reduced.

The two stops are preferably constituted by plate-like or rod-like fingers. The stack can be placed onto the stops, but it is also possible to place the stops onto the stack from above, wherein the stops can then be tensioned against the stack by means of spring force.

Further characteristics of the device can be derived from the description of the method provided above. These characteristics are not mentioned a second time to avoid repetitions.

Further details and characteristics of the invention can be seen from the following description of embodiments with reference to the drawing. The figures show:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a schematic representation of the inventive device with a stack to be banded before application of the tensioning force;

FIG. 2 the stack according to FIG. 1 after the strap has been tensioned;

FIG. 3 the stack according to FIG. 2 immediately before the stack is further transported;

FIG. 4 the stack according to FIG. 3 after separation from the stops;

FIG. 5 overextension of the strap with a very thin stack; and

FIG. 6 an alternative configuration of the stops.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a stack 10 consisting of several wide flat products 17 lying one upon the other, for example, envelopes. Stack 10 has a cuboidal shape and lies with its underside in contact with two plate-like fingers 14 in such a way that the outer edges facing away from each other of the fingers 14 are directly next to the outer edges facing away from each other of stack 10, i.e. each ending flush with a side edge of the stack 10. The fingers 14 form stops 13 for a strap 11 that is to be wound around the stack 10.

The strap 11 is held at one of its ends via an only schematically depicted holder 12 and is wound completely around the stack 10 at a distance therefrom, wherein the free end of the strap 11 opposite the holder 12 is again in the region of the holder 12 resulting in an overlap 15 of the strap in this region. After the strap 11 has been wound around the stack 10, a tensile force is exerted on the free end of the strap 11, as is indicated by the arrow Z in FIG. 1. Because of the tensile force Z, the strap 11 comes to rest closely fitting around the stack 10 and around the stops 13 and is tensioned inward onto the stack 10, wherein, however, the tensioning movement of the strap 11 is limited by the stops 13. As FIG. 2 shows, the stack 10 is pressed together by the tensioned strap 11 in the vertical direction, i.e. in the stacking direction, but the stops 13 prevent the tensioning force from being able to deform the stack 10 in the plane of the individual wide products 17.

After the strap 11 has reached the tensioned position, the strap 11 is fixed in the overlap region 15, for example, by a weld, as indicated by the arrows S in FIG. 2. In this condition, the stack 10 is held together to form a unit by the strap 11 wherein, however, the fingers 14 constituting the stops 13 are disposed within the ring formed by the strap 11 and wherein the strap 11 still exerts a tensioning force on the stops 13.

The stops 13 can be repositioned relative to each other. As FIG. 3 shows, the fingers 14 constituting the stops 13 can be moved toward each other, i.e. toward the vertical center plane of the stack 10, as indicated by the arrows A in FIG. 3. In this way, the tensioning force that the strap 11 exerts on the fingers 14 is reduced so that the stack 10 banded by the strap 11 in this condition can easily be pulled off the fingers 14 perpendicularly to the plane of the drawing. After the stack 10 has been pulled from the fingers 14, a transportation unit that can be handled by usual methods in the form of a stack 10 of wide, flat products 17 is formed that is held together by the circumferential strap 11, as shown in FIG. 4.

FIG. 5 shows a stack 10 comprising only two thin wide products 17, for example, envelopes, wherein the problem occurs that the strap 11 at the edges of the stack 10, because of its high internal rigidity, is not deflected sharply enough to follow the contour of the stack 10 with a close fit. To compensate for this, the fingers 14 forming the stops 13 are repositioned outward relative to each other, as indicated by the arrows B in FIG. 5. Therein, the fingers 14 are repositioned beyond the outer contour of the stack 10 in the outward direction and exert a further tensioning force on the already tensioned and fixed strap 11 in the outer deflection regions that results in high local stresses at the outer edges of the stops 14 whereby the strap 11 is overextended in this region and plastically deformed. Because of the overextension of the strap, the internal rigidity of the strap 11 is reduced in this region to the point that the strap is sharply deflected and can thus follow the contour of the thin stack 10.

In the embodiments illustrated so far, the stack was placed onto the fingers 14 forming the stops 13 and the overlap region 15 of the strap 11, in which the strap ends are connected to each other, is formed underneath the stack 10 between the two fingers 14. FIG. 6 shows an alternative embodiment in which the stack 10 is prepositioned and the fingers 14 constituting the stops 13 are then applied from above, for example, by means of the force of one spring 16 each, indicated only by an arrow, onto the edge regions of the stack 10 facing away from each other, whereupon tensioning of the strap 11, including any possible local overextension of the strap 11, is performed in the way described above. 

I claim:
 1. A method for banding a stack of wide, flat products with a strap, the method comprising the steps of: a) winding the strap completely around the stack; b) positioning at least two stops on or near the stack to limit a tensioning movement of the strap; c) exerting, following steps a) and b), a tensile force on the strap, thereby tensioning the strap in an inward direction onto the stack; d) fixing the strap following step c); e) repositioning the stops relative to each other following step d); and f) removing the stops from the stack following step e).
 2. The method of claim 1, wherein both stops are repositioned.
 3. The method of claim 1, wherein the stops are moved away from each other.
 4. The method of claim 1, wherein the stops are moved toward each other.
 5. The method of claim 1, wherein after fixture of the strap, the stops are repositioned relative to each other in such a way that the strap is locally overextended and plastically deformed.
 6. The method of claim 1, wherein the stops are positioned in edge regions of the stack on opposite sides thereof.
 7. The method of claim 6, wherein the stops are each disposed flush with one side edge of the stack before the strap is tensioned.
 8. The method of claim 1, wherein, before withdrawal of the stack, the stops are repositioned relative to each other in such a way that the strap exerts no or much reduced force on the stops.
 9. The method of claim 1, wherein the stack is pulled from the stops after fixture of the strap.
 10. A device for banding a stack of wide, flat products with a strap, the device comprising: a tensioning unit, said tensioning unit structured to wind the strap completely around the stack, to tension the strap inwardly onto the stack and to fix the strap; two stops, which limit a tensioning movement of the strap and onto which the strap can be applied in a tensioned condition; and a mechanism for repositioning the stops relative to each other.
 11. The device of claim 10, wherein a distance between the stops can be enlarged and/or reduced.
 12. The device of claim 10, wherein the stops are constituted by plate-like or rod-like fingers.
 13. The device of claim 10, wherein the stack can be placed onto the stops.
 14. The device of claim 10, wherein the stops can be placed onto the stack from above. 